1. Field of the Invention
The invention relates to a motion detector or proximity switch for detecting moving objects, wherein a high-frequency electromagnetic radiation is produced via a freely oscillating oscillator and is emitted via a transmitting antenna, and the radiation reflected from the moving object and modified due to the Doppler effect is detected with regard to change in its phase angle or amplitude via a receiving antenna and is compared in an evaluation device with the parameters of the emitted radiation for the production of an output signal,.
2. Background Art
Motion detectors of the type in question are used, for example, for spatial monitoring. They serve accordingly as a type of proximity switch. They are used, for example, as automatic door openers, which detect the approach of a person and generate a signal triggering a control signal to the door opening device.
Motion detectors are also known which automatically switch on the lighting in the exterior region of houses and internal spaces as people approach.
In other applications it is proposed to use motion detectors for spatial monitoring in conjunction with alarm systems.
Many known motion detectors work on the basis of light barriers or by detecting infrared radiation emitted by people.
Both methods have the disadvantage, particularly for use as alarm systems, that they can be easily recognized due to the required construction size and can accordingly therefore also be manipulated. Furthermore, the known methods have the inherent disadvantage that they are sensitive to light and temperature, making them prone to faults and only usable under certain conditions.
Motion detectors are also already known which work by using the Doppler effect. DE 39 22 165 A1 describes, for example, a Doppler radar sensor which is arranged as a planar circuit on a substrate with an antenna on the top of the substrate and an evaluation unit connected after the sensor. The sensor emits continuous or pulsed signals in the microwave range (3 to 30 gigahertz) via an antenna. These signals are reflected by objects moved in the radiation field and, displaced by the Doppler frequency, picked up again by the antenna and detected by the evaluation unit.
Up until now motion detectors of the type described were used as separate apparatus on doors, walls or ceilings due to their mode of construction. For this reason they are often exposed to manipulation, deliberate damage or even destruction. Moreover, conventional motion detectors of the type in question have a very high power requirement, being dependent on a continuous power supply, an emergency power supply, if available, being only temporarily available, e.g. from a battery or an accumulator.